This invention relates to a two-component polyurethane adhesive containing as resin a polyol produced largely from renewable, natural raw materials.
Polyurethane adhesives have been known for years and are widely used. Of particular importance in this respect, particularly for technical applications, are the two-component adhesives which are stirred and mixed together by the user before bonding to form a reaction mixture which subsequently hardens after application to the substrates to be bonded. Two-component polyurethane adhesives such as these consist of an isocyanate component having a functionality of 2 and higher, as a hardener, and of a resin, more especially a polyol. Numerous polyhydric alcohols have already been proposed as resins for two-component polyurethane adhesives, including castor oil as a natural, renewable product. Castor oil is a fatty acid triglyceride which on average contains 2.7 secondary OH-groups per molecule, the fatty acid being predominately ricinoleic acid.
Although castor oil has recently acquired some significance as a resin for two-component polyurethane adhesives and is used in particular for flexible solid adhesives, it does have the disadvantage that adhesives produced therefrom frequently show an excessively short pot life. Another disadvantage lies in the dependence upon only a single raw material. This is both an economic disadvantage and, more particularly, a technical disadvantage, i.e., castor oil is not variable in regard to the number of OH-groups present or can only be processed by elaborate reactions to form products having relatively high OH numbers for example.